Why do Harley riders have floating heads?

I can still lay down on my tank and tilt my head all the way back, looking through the top of my eyes if want to.

I guess this one is all over the interwebs, but I saw it on a Ducati mailing list: “Watching NASCAR is like tossing Skittles in the toilet and flushing.”
Though I must admit the new pastels being sported in MotoGP and WSB are stunning.